Reflection and refraction optical system and projection exposure apparatus using the same

ABSTRACT

A reflection and refraction optical system includes a polarization beam splitter, a concave mirror, a lens group and a quarter waveplate, wherein an additional waveplate is provided to transform S-polarized light from the polarization beam splitter into circularly polarized light.

FIELD OF THE INVENTION AND RELATED ART

[0001] This invention relates generally to an imaging optical systemsuch as a reflection and refraction optical system and, moreparticularly, to a reflection and refraction optical system usable forimaging a fine pattern in manufacture of microdevices such assemiconductor devices (such as ICs or LSIs), image pickup devices (suchas CCDs) or display devices (such as liquid crystal panels). In anotheraspect, the invention is concerned with a projection exposure apparatususing such a reflection and refraction optical system.

[0002] The degree of integration of a semiconductor device such as IC orLSI is increasing, and the fine processing technology for asemiconductor wafer is being developed considerably. In the projectionexposure technique which is the main of the fine processing technology,the resolution has been increased to a level allowing formation of animage of a linewidth not greater than 0.5 micron.

[0003] The resolution can be improved by shortening the wavelength oflight used for the exposure process. However, the shortening ofwavelength restricts the glass materials usable for a projection lenssystem, and correction of chromatic aberration becomes difficult toattain.

[0004] A projection optical system with which the difficulty ofcorrecting chromatic aberration can be reduced, may be a reflection andrefraction optical system comprising a concave mirror and a lens group,wherein the imaging function mainly attributes to the power of theconcave mirror.

[0005] Such reflection and refraction optical system may include apolarization beam splitter, a quarter waveplate and a concave mirror,disposed in this order from the object plane side. Light from the objectplane may go by way of the polarization beam splitter and the quarterwaveplate, it may be reflected by the concave mirror. After this, thelight may go again by way of the quarter waveplate and the polarizationbeam splitter, and it may be imaged upon an image plane. The combinationof polarization beam splitter and quarter waveplate may effective toreduce the loss of light. However, use of rectilinearly polarized lightfor the imaging process may involve a problem in the formation of a fineimage of a linewidth not greater than 0.5 micron that the imagingperformance may change in dependence upon the orientation (lengthwisedirection) of a (linear) pattern on the object plane.

[0006] As an example, the contrast of an image of 0.2 micron, which canbe formed by using a projection optical system of a numerical aperture(N.A.) of 0.5 and a design wavelength 248 nm together with a phase shiftmask (line-and-space pattern), is changeable by about 20%, depending onwhether the direction of polarization of light used for the imagingprocess is parallel to or perpendicular to the lengthwise direction ofthe pattern.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide an improvedimaging optical system effective to solve such problem as describedabove.

[0008] It is another object of the present invention to provide animproved reflection and refraction optical system effective to solvesuch problem as described above.

[0009] It is a further object of the present invention to provide animproved projection exposure apparatus which is free from such problemdescribed above.

[0010] An imaging optical system according to the present invention mayinclude a polarization beam splitter, a quarter waveplate and areflection mirror which may be disposed in this order from an objectplane. Light from the object plane may go by way of the polarizationbeam splitter and the quarter waveplate, and it may be reflected by thereflection mirror. The reflected light may go again by way of thequarter waveplate and the polarization beam splitter, and then it may beimaged upon an image plane. Means may be provided between thepolarization beam splitter and the image plane, for changing the planeof polarization of polarized light from the polarization beam splitter.

[0011] A reflection and refraction optical system according to thepresent invention may include a polarization beam splitter, a quarterwaveplate and a concave reflection mirror which may be disposed in thisorder from an object plane. Light from the object plane may go by way ofthe polarization beam splitter and the quarter waveplate, and it may bereflected by the concave reflection mirror. The reflected light may goagain by way of the quarter waveplate and the polarization beamsplitter, and then it may be imaged upon an image plane. Means may beprovided between the polarization beam splitter and the image plane, forchanging the plane of polarization of polarized light from thepolarization beam splitter.

[0012] A projection exposure apparatus according to the presentinvention may include projection optical system for projecting a patternof a mask onto a substrate to be exposed. The projection optical systemmay comprises a polarization beam splitter, a quarter waveplate and aconcave reflection mirror which may be disposed in this order from themask. Light from the mask may go by way of the polarization beamsplitter and the quarter waveplate, and it may be reflected by theconcave reflection mirror. The reflected light may go again by way ofthe quarter waveplate and the polarization beam splitter, and then itmay be directed to the substrate such that the pattern of the mask maybe imaged upon the substrate. Means may be provided between thepolarization beam splitter and the image plane, for changing the planeof polarization of polarized light from the polarization beam splitter.

[0013] A reflection and refraction optical system or a projectionexposure apparatus according to the present invention may suitably usedfor manufacture of microdevices such as semiconductor devices (such asICs or LSIs), image pickup devices (such as CCDs) or display devices(such as liquid crystal panels). Particularly, a reflection opticalsystem of the present invention when arranged to provide a reductionmagnification and used as a projection optical system in combinationwith deep ultraviolet light, may be effective to image a fine devicepattern of a linewidth not greater than 0.5 micron.

[0014] These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic view of a reduction projection exposureapparatus for manufacture of semiconductor devices, according to anembodiment of the present invention.

[0016]FIG. 2 is a flow chart of semiconductor device manufacturingprocesses.

[0017]FIG. 3 is a flow chart, illustrating details of a wafer process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018]FIG. 1 illustrates a reduction projection exposure apparatusaccording to an embodiment of the present invention, for manufacture ofsemiconductor devices.

[0019] Denoted in FIG. 1 at 1 is a reticle having a circuit pattern tobe transferred to a wafer 9 for manufacture of semiconductor devices.The reticle 1 is held on an object plane of a reflection and refractionoptical system 100, by means of a reticle stage (not shown). The circuitpattern of the reticle 1 can be illuminated with deep ultraviolet lightof a wavelength λ (<300 (nm)) from an illumination system (not shown),with uniform illuminance. Divergent light from the illuminated reticle1, including zeroth order and first order diffraction lights, isreceived by a first lens group 2 having a positive refracting power. Thefirst lens group 2 serves to transform the received divergent light intoa parallel light consisting of a flux of light rays parallel to theoptical axis AX, and it projects the light on a polarization beamsplitter 3. The parallel light incident on the polarization beamsplitter 3 passes through the same, and then it passes through a quarterwaveplate 4 and enters a second lens group 5 having a negativerefracting power.

[0020] The parallel light passing through the polarization beam splitter3 and impinging on the lens group 5 is P-polarized light with respect tothe dividing plane 3 a of the polarization beam splitter 3. Of theparallel light impinging on the polarization beam splitter 3, the lightwhich is S-polarized light with respect to the dividing plane 3 a isreflected by that plane 3 a upwardly as viewed in the drawing.

[0021] Further, the quarter waveplate 4 is arranged and disposed so asto transform P-polarized light, entering it from the left hand side inthe drawing, into circularly polarized light and also to transformcircularly polarized light, entering it from the right hand side in thedrawing, into S-polarized light.

[0022] The second lens group serves to transform the parallel light,passing through the polarization beam splitter 3 and the quarterwaveplate 4, into divergent light and to project the same on a concavemirror 6. The concave mirror 6 has a spherical reflection surface whichis rotationally symmetrical with respect to the optical axis AX. Theconcave mirror 6 serves to reflect and converge the received divergentlight back to the lens group 5. The light goes by way of the second lensgroup 5 and the quarter waveplate 4, and it is projected to thepolarization beam splitter 3. Due to the function of the quarterwaveplate 4, the light reflected and converged by the concave mirror 6and impinging again on the polarization beam splitter 3 is S-polarizedlight with respect to the dividing plane 3 a. As a consequence, thisre-entering light is reflected by the dividing plane 3 a of thepolarization beam splitter 3 downwardly as viewed in the drawing.

[0023] Disposed below the polarization beam splitter 3 are apolarization plane changing means 7 and a third lens group 8 having apositive refracting power. Further below the third lens group 3, thereis a silicon wafer 9 for manufacture of semiconductor devices whichwafer is held by a movable X-Y stage (not shown) so that its surface, tobe exposed, coincides with the image plane of the reflection andrefraction optical system 100.

[0024] The polarization plane changing means 7 comprises a quarterwaveplate which serves to transform the light, reflected by the dividingplane 3 a of the polarization beam splitter 3, into circularly polarizedlight which in turn is projected on the third lens group 8. The thirdlens group 8 serves to collect the circularly polarized light from thequarter waveplate of the polarization plane changing means 7, and areduced image of the circuit pattern of the reticle 1 is formed on thewafer 9.

[0025] The projection exposure apparatus of this embodiment uses apolarization beam splitter (3), but it is arranged to form an imagethrough circularly polarized light. As a consequence, for imaging finepatterns, there does not occur non-uniformness of resolution betweendifferent patterns which might otherwise result from the polarizationdependency of pattern. In other words, the projection exposure apparatusof this embodiment assures constant resolution independently of the type(orientation) of the fine pattern of a reticle 1 used.

[0026] In the projection exposure apparatus of this embodiment, thereticle stage for supporting the reticle 1 may be disposed horizontallyand a reflection mirror may be provided between the reticle stage andthe lens group 2 so as to deflect the optical axis AX by 45 deg. In thatoccasion, the overall size of the apparatus can be made small.

[0027] The projection exposure apparatus of this embodiment may bearranged to execute step-and-repeat exposures according to which the X-Ystage on which the wafer 9 is placed is moved stepwise to form circuitpatterns on substantially the whole surface of the wafer 9.Alternatively, it may be arranged to execute step-and-scan exposureswherein the X-Y stage on which the wafer 9 is place is moved stepwiseand scanningly.

[0028] The projection exposure apparatus of this embodiment may be usedin combination with a phase shift mask as the reticle 1. In thatoccasion, it may be possible to image a pattern of a smaller linewidth.Further, the structure of the illumination system (not shown) may bemodified into an oblique illumination system by which the reticle 1 isilluminated along a direction inclined with respect to the optical axisAX. Also in that occasion, a pattern of smaller linewidth may be imaged.

[0029] The projection exposure apparatus of this embodiment may use alight source comprising a KrF excimer laser (λ≅248 nm), an ArF excimerlaser (λ≅193 nm) or an ultra high pressure Hg lamp (emission linespectrum: λ≅250 nm), for example.

[0030] In another embodiment according to the present invention, aprojection exposure apparatus such as described above may include apolarization plane changing means 7 comprising a half waveplate beingmade rotatable about the optical axis AX. When such polarization planechanging means is used, it is possible to change the plane ofpolarization of light from the polarization beam splitter 3 inaccordance with the orientation of a fine pattern of a reticle 1 used.Thus, imaging with polarization light of increased resolution(non-deteriorated resolution) may always be assured.

[0031] For example, in an occasion where a fine pattern of a reticle 1has a lengthwise direction laid longitudinally (up and down) as viewedin the drawing, the rotational angle of the half waveplate 7 may be soset as to transform the plane of polarization of the light from thepolarization beam splitter 3, from S-polarized light into P-polarizedlight.

[0032] In an occasion where a fine pattern of a reticle 1 has alengthwise direction laid perpendicularly to the sheet of the drawing,the rotational angle of the half waveplate 7 may be set so as to retainthe plane of polarization (S-polarization) of the light from thepolarization beam splitter 3.

[0033] In an occasion where a fine pattern of a reticle 1 has anorientation, extending both longitudinally as viewed in the drawing andperpendicular to the sheet of the drawing, (i.e., a cross pattern), therotational angle of the half waveplate 7 may be so set as to transformthe plane of polarization (S-polarization) of the light from thepolarization beam splitter 3, into polarized light of 45 deg. withrespect to both of the S-polarization and P-polarization.

[0034] In a further embodiment according to the present invention, thewaveplate of the polarization plane changing means 7 may comprise anelectro-optic crystal device (EO optical-modulator) whose birefringence(double refraction) characteristic can be controlled electrically.

[0035] Next, an embodiment of a method of manufacturing semiconductordevices based on the reticle 1 and the projection exposure apparatus ofFIG. 1, will be explained.

[0036]FIG. 2 is a flow chart of the sequence of manufacturing asemiconductor device such as a semiconductor chip (e.g. IC or LSI), aliquid crystal panel or a CCD, for example. Step 1 is a design processfor designing the circuit of a semiconductor device. Step 2 is a processfor manufacturing a mask on the basis of the circuit pattern design.Step 3 is a process for manufacturing a wafer by using a material suchas silicon.

[0037] Step 4 is a wafer process which is called a pre-process wherein,by using the so prepared mask and wafer, circuits are practically formedon the wafer through lithography. Step 5 subsequent to this is anassembling step which is called a post-process wherein the waferprocessed by step 4 is formed into semiconductor chips. This stepincludes assembling (dicing and bonding) and packaging (chip sealing).Step 6 is an inspection step wherein operability check, durability checkand so on of the semiconductor devices produced by step 5 are carriedout. With these processes, semiconductor devices are finished and theyare shipped (step 7).

[0038]FIG. 3 is a flow chart showing details of the wafer process. Step11 is an oxidation process for oxidizing the surface of a wafer. Step 12is a CVD process for forming an insulating film on the wafer surface.Step 13 is an electrode forming process for forming electrodes on thewafer by vapor deposition. Step 14 is an ion implanting process forimplanting ions to the wafer. Step 15 is a resist process for applying aresist (photosensitive material) to the wafer. Step 16 is an exposureprocess for printing, by exposure, the circuit pattern of the mask onthe wafer through the exposure apparatus described above. Step 17 is adeveloping process for developing the exposed wafer. Step 18 is anetching process for removing portions other than the developed resistimage. Step 19 is a resist separation process for separating the resistmaterial remaining on the wafer after being subjected to the etchingprocess. By repeating these processes, circuit patterns are superposedlyformed on the wafer.

[0039] As described hereinbefore, the present invention in an aspectthereof provides an imaging optical system or a reflection andrefraction optical system, by which high resolution is assuredindependently of the type (orientation) of a fine pattern of an objectto be projected. Thus, the present invention in another aspecteffectively assures an improved projection exposure apparatus havingsuperior projection exposure performance and based on a reflection andrefraction optical system, or a method of manufacturing various devicesthrough use of a reflection and refraction optical system.

[0040] While the invention has been described with reference to thestructures disclosed herein, it is not confined to the details set forthand this application is intended to cover such modifications or changesas may come within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An imaging optical system, comprising: apolarization beam splitter; a quarter waveplate; a reflection mirror;and polarization plane changing means; wherein a beam from an objectplane is projected by way of said polarization beam splitter and saidquarter waveplate upon said reflection mirror, wherein the projectedbeam is reflected by said reflection mirror and is projected by way ofsaid quarter waveplate and said polarization beam splitter upon an imageplane, and wherein said polarization plane changing means is disposedbetween said polarization beam splitter and the image plane to changethe plane of polarization of the beam from said beam splitter.
 2. Animaging optical system according to claim 1 , wherein said reflectionmirror comprises a concave mirror.
 3. An imaging optical systemaccording to claim 2 , further comprising a first lens group disposedbetween the object plane and said polarization beam splitter and a thirdlens group disposed between said polarization beam splitter and theimage plane.
 4. An imaging optical system according to claim 3 , whereinsaid first lens group is effective to transform a beam from the objectplane into a parallel beam and to project the parallel beam to saidpolarization beam splitter.
 5. An imaging optical system according toclaim 4 , further comprising a second lens group disposed between saidpolarization beam splitter and said reflection mirror, wherein saidsecond lens group is effective to transform the parallel beam from saidpolarization beam splitter into a divergent beam and to direct the sameto said reflection mirror.
 6. An imaging optical system according toclaim 3 , wherein said polarization plane changing means is disposedbetween said polarization beam splitter and said third lens group.
 7. Animaging optical system according to claim 1 , wherein said polarizationplane changing means comprises a second quarter waveplate effective totransform a beam from said polarization beam splitter into a circularlypolarized beam.
 8. An imaging optical system according to claim 1,wherein said polarization plane changing means comprises a halfwaveplate effective to transform a beam from said polarization beamsplitter into a rectilinearly polarized beam, being polarized in adesired direction.
 9. An imaging optical system, comprising: apolarization beam splitter; a first quarter waveplate; a concave mirror;and a second quarter waveplate; wherein a beam from an object plane isprojected by way of said polarization beam splitter and said firstquarter waveplate upon said concave mirror, wherein the projected beamis reflected by said concave mirror and is projected by way of saidfirst quarter waveplate and said polarization beam splitter upon animage plane, and wherein said second quarter waveplate is disposedbetween said polarization beam splitter and the image plane to changethe beam from said beam splitter to a circularly polarized beam.
 10. Animaging optical system according to claim 9 , further comprising a firstlens group disposed between the object plane and said polarization beamsplitter and a third lens group disposed between said polarization beamsplitter and the image plane.
 11. An imaging optical system according toclaim 10 , wherein said first lens group is effective to transform abeam from the object plane into a parallel beam and to project theparallel beam to said polarization beam splitter.
 12. An imaging opticalsystem according to claim 11 , further comprising a second lens groupdisposed between said polarization beam splitter and said concavemirror, wherein said second lens group is effective to transform theparallel beam from said polarization beam splitter into a divergent beamand to direct the same to said concave mirror.
 13. An imaging opticalsystem according to claim 10 , wherein said second quarter waveplate isdisposed between said polarization beam splitter and said third lensgroup.
 14. An imaging optical system, comprising: a polarization beamsplitter; a quarter waveplate; a concave mirror; and a half waveplate;wherein a beam from an object plane is projected by way of saidpolarization beam splitter and said quarter waveplate upon said concavemirror, wherein the projected beam is reflected by said concave mirrorand is projected by way of said quarter waveplate and said polarizationbeam splitter upon an image plane, and wherein said half waveplate isdisposed between said polarization beam splitter and the image plane tochange the beam from said beam splitter to a linearly polarized beam,being polarized in a desired direction.
 15. An imaging optical systemaccording to claim 14 , further comprising a first lens group disposedbetween the object plane and said polarization beam splitter and a thirdlens group disposed between said polarization beam splitter and theimage plane.
 16. An imaging optical system according to claim 15 ,wherein said first lens group is effective to transform a beam from theobject plane into a parallel beam and to project the parallel beam tosaid polarization beam splitter.
 17. An imaging optical system accordingto claim 16 , further comprising a second lens group disposed betweensaid polarization beam splitter and said concave mirror, wherein saidsecond lens group is effective to transform the parallel beam from saidpolarization beam splitter into a divergent beam and to direct the sameto said concave mirror.
 18. An imaging optical system according to claim15 , wherein said half waveplate is disposed between said polarizationbeam splitter and said third lens group.
 19. A projection exposureapparatus for projecting a pattern of an original onto a substrate, saidapparatus comprising: a polarization beam splitter; a quarter waveplate;a reflection mirror; and polarization plane changing means; wherein abeam from the original is projected by way of said polarization beamsplitter and said quarter waveplate upon said reflection mirror, whereinthe projected beam is reflected by said reflection mirror and isprojected by way of said quarter waveplate and said polarization beamsplitter upon the substrate, and wherein said polarization planechanging means is disposed between said polarization beam splitter andthe substrate to change the plane of polarization of the beam from saidbeam splitter.
 20. An apparatus according to claim 19 , wherein saidreflection mirror comprises a concave mirror.
 21. An apparatus accordingto claim 20 , further comprising a first lens group disposed between theoriginal and said polarization beam splitter and a third lens groupdisposed between said polarization beam splitter and the substrate. 22.An apparatus according to claim 21 , wherein said first lens group iseffective to transform a beam from the original into a parallel beam andto project the parallel beam to said polarization beam splitter.
 23. Anapparatus according to claim 22 , further comprising a second lens groupdisposed between said polarization beam splitter and said reflectionmirror, wherein said second lens group is effective to transform theparallel beam from said polarization beam splitter into a divergent beamand to direct the same to said reflection mirror.
 24. An apparatusaccording to claim 21 , wherein said polarization plane changing meansis disposed between said polarization beam splitter and said third lensgroup.
 25. An apparatus according to claim 18 , wherein saidpolarization plane changing means comprises a second quarter waveplateeffective to transform a beam from said polarization beam splitter intoa circularly polarized beam.
 26. An apparatus according to claim 19 ,wherein said polarization plane changing means comprises a halfwaveplate effective to transform a beam from said polarization beamsplitter into a rectilinearly polarized beam, being polarized in adesired direction.
 27. A device manufacturing method for manufacturingmicrodevices on the basis of a projection exposure apparatus as recitedin any one of claims 19-26, and further comprising projecting a devicepattern of an original onto a substrate to transfer the former to thelatter.
 28. A projection exposure apparatus for projecting a pattern ofan original onto a substrate, comprising: a polarization beam splitter;a first quarter waveplate; a concave mirror; and a second quarterwaveplate; wherein a beam from the original is projected by way of saidpolarization beam splitter and said first quarter waveplate upon saidconcave mirror, wherein the projected beam is reflected by said concavemirror and is projected by way of said first quarter waveplate and saidpolarization beam splitter upon the substrate, and wherein said secondquarter waveplate is disposed between said polarization beam splitterand the substrate to change the beam from said beam splitter to acircularly polarized beam.
 29. An apparatus according to claim 28 ,further comprising a first lens group disposed between the original andsaid polarization beam splitter and a third lens group disposed betweensaid polarization beam splitter and the substrate.
 30. An apparatusaccording to claim 29 , wherein said first lens group is effective totransform a beam from the original into a parallel beam and to projectthe parallel beam to said polarization beam splitter.
 31. An apparatusaccording to claim 30 , further comprising a second lens group disposedbetween said polarization beam splitter and said concave mirror, whereinsaid second lens group is effective to transform the parallel beam fromsaid polarization beam splitter into a divergent beam and to direct thesame to said concave mirror.
 32. An apparatus according to claim 29 ,wherein said second quarter waveplate is disposed between saidpolarization beam splitter and said third lens group.
 33. A devicemanufacturing method for manufacturing microdevices on the basis of aprojection exposure apparatus as recited in any one of claims 28-32, andfurther comprising projecting a device pattern of an original onto asubstrate to transfer the former to the latter.
 34. A projectionexposure apparatus for projecting a pattern of an original onto asubstrate, comprising: a polarization beam splitter; a quarterwaveplate; a concave mirror; and a half waveplate; wherein a beam fromthe original is projected by way of said polarization beam splitter andsaid quarter waveplate upon said concave mirror, wherein the projectedbeam is reflected by said concave mirror and is projected by way of saidquarter waveplate and said polarization beam splitter upon thesubstrate, and wherein said half waveplate is disposed between saidpolarization beam splitter and the substrate to change the beam fromsaid beam splitter to a linearly polarized beam, being polarized in adesired direction.
 35. An apparatus according to claim 34 , furthercomprising a first lens group disposed between the original and saidpolarization beam splitter and a third lens group disposed between saidpolarization beam splitter and the substrate.
 36. An apparatus accordingto claim 35 , wherein said first lens group is effective to transform abeam from the original into a parallel beam and to project the parallelbeam to said polarization beam splitter.
 37. An apparatus according toclaim 36 , further comprising a second lens group disposed between saidpolarization beam splitter and said concave mirror, wherein said secondlens group is effective to transform the parallel beam from saidpolarization beam splitter into a divergent beam and to direct the sameto said concave mirror.
 38. An apparatus according to claim 35 , whereinsaid half waveplate is disposed between said polarization beam splitterand said third lens group.
 39. A device manufacturing method formanufacturing microdevices on the basis of a projection exposureapparatus as recited in any one of claims 34-38, and further comprisingprojecting a device pattern of an original onto a substrate to transferthe former to the latter.
 40. A method according to claim 27 , whereinthe original is illuminated with light projected obliquely thereon. 41.A method according to claim 27 , wherein the original comprises a phaseshift mask.
 42. A method according to claim 33 , wherein the original isilluminated with light projected obliquely thereon.
 43. A methodaccording to claim 33 , wherein the original comprises a phase shiftmask.
 44. A method according to claim 39 , wherein the original isilluminated with light projected obliquely thereon.
 45. A methodaccording to claim 39 , wherein the original comprises a phase shiftmask.